1. Technical Field
The inventive concept relates to a boost circuit and an image sensor, and more particularly, to a boost circuit capable of controlling inrush current and an image sensor using a boosting voltage output from the boost circuit.
2. Description of Related Art
Recently, as electronic products with a photography function such as camcorders, digital cameras, and mobile phones have been made compact and slim, the size of a power supply unit, for example, a battery, has been reduced. Accordingly, a load on the power supply unit which supplies power to an image sensor included in these electronic products increases so that it is difficult to secure a sufficient power margin of the power supply unit.
To reduce the production costs of electronic product sets, power management units and various power supply units are integrally used. Accordingly, inrush current increases during driving each sub-block so that supply of power to other sub-blocks using the same power source from the power supply unit may be unstable. When the supply of power is unstable, a data hold error may be generated in a logic block and a characteristic error of settling time may occur in an analog block, so that the overall system may malfunction.
In particular, to prevent characteristic deterioration according to the miniaturization of the pitch of a pixel of an image sensor, a boost circuit is used to generate a high voltage over a power voltage. Using the boost circuit may cause the problem of inrush current. Generally, the boost circuit uses a voltage boosting regulator including an internal capacitor and an external capacitor for initial charge. The inrush current during the initial charge may deteriorate the function and characteristic during driving of the electronic product set and image sensor.
Also, to cope with an increase in load according to an increase in resolution of the image sensor, an increase in capacity of the capacitor for stabilization of output voltage of the boost circuit is needed. The amount of inrush current may be further increased to charge the capacitor in the initial stage when supply of power starts.
Accordingly, in a typical boost circuit, a considerable amount of inrush current is generated to charge the capacitor of the boost circuit in the initial stage when supply of power starts.